Tuning means



Sept. 15, 1931.

H. O. PETERSON TUNING MEANS Filed March 2'7. 1929 INVENTOR wow 0. PETERSON ATTORNEY Patented Sept. 15, 1931 UNITED STATES PATENT OFFICE HAROLD 0..PIEI'JIEEQOL'I',v OE RIVEBHEAD, N-EW YOBK ASSIGNOR TO RADIO CORPORATION OE AMERIGA, A CORPORATION OF DELAWARE TUNING MEANS.

Applicationfiled March 27, 1928. Serial no. 350,149.

This invention-:relatemto tuningmeans, and more particularly to a: tuning condenser for use. in. shortwave radio equipment.

When constructing apparatus foruse: with very short. waves, factors which ordinarily are negligible, such as; the stray capacitance between a circuit and ground, become very appreciable, and must be accounted for in ad- Vance: The difliculfliesare: overcome-to a. conn siderable extent by employing symmetrical circuits, such aspushpull electron emission tube: circuits. However, at the extreme fre quencieshere considered, I have found that thebalance of such circuits may be upset by the=d ifierenee in themagnitudeof the stray capacitance at the twosidesoi a tuning-com denser with! respect toground. Furthermore, during: tuning, or movement of. the condens er rotor, the amount oat this unbalance continuelly varies thus complicating the prob lemt To overcome-this difiiculty it hasrbeen suggested to use two equalv condensers. connected. in -This, however, halves. the total n amount of. tuning eapacitanceandat the-same time: doubles the total amount oat stray capacitance, thereby quadnupling the ratio. of stmay capacitance to tuning capacitance, whereas this: ratio should be. a minimum, es-

791 peciallywhen leading with exceedingly high.

frequencies. in. order to preventhigh. losses.

The object. of. my invention is: to provide. a. tuning reactance the. stray capacitance of which isbalancedor symmetrical, and which. remains so even. during movement of the rotor, but which at the same time is small in magnitude rel'at'ive to the magnitude of the tuning capacitance. This object I fulfill by providing a tuning reactanceconsisting, structurally, oftwo similar stationary portions, similar movable-portions cooperatiug therewith, means for simultaneously and. equally moving the movable portions, and mans connecting each of the stationary p'or tions with that movable portion, which cooperates with the other stationary portion. 'llhccondensers awe-thins connectedin parallel, so that the ratio of. stray capacitancetotun.- ing capacitancais not increased. Atthe same. 5.0; time, each terminal. oi the. condenser being connected to both a stationary portion. and a. movable portion, the stray capacitances betweeneach terminal and ground remain equal.

In apreferred? modification I provide a shielding compartment, and a tuning condenser for the resonant circuit of a push-pull electron: emission tube stage comprising, structurally, two similar'condensers arranged symmetrically with respect to the walls of the'compartment andmechanically connected for unicontroL. The rotors are electrically insulated, and each of the rotors is connected Withthe stator of the other condenser, sothat each side of the condenser consists of a rotor and a stator, in'whichcase the stray capaci- 66; tancebetween the tuning condenser and the shield obviously is: symmetrical even during. movement of the condenser rotors.

My inyention is described morein' detail in the following specification, which is accom- 70. panied by a drawing; in which. Figure 1 is a wiring. diagram explanatory of my invention; Figure 2 is a schematic representation of one form of condenser;- and Figure 3 illustrates a preferred! modification.

Referring, to Figure I, there are. a pair of. electron emission tubes 42 and 4.4, to: which a: resonant circuit 46- issymmetrically coupl'ed. In" this case" the circuit 46 is an input circuit connected to the control electrodes of so the tubes. The circuit is arranged symmetrically, an d therefore the'mid point of'the input and output inductances may be grounded with respect to radio: frequency, preferably through blocking condensers, as shown, in order not to short circuit the'potential sources for biasing thecontrol electrodes and polarizing the'an-od'es of the tubes;

The symmetry of the circuit is designed with a view to providingcqual stray capacitancefrom'ea ch: side of the circuit'to ground. This stray capacitance has been represented by the condensers 50 and 52. It will be understood without diliiculty'that with the usual type of tuning condenser this symmetry will be upset, owing to the inequality of the stray capacitances of the stator and of. the rotor of the tuning condenser. This inequality will cause a, difference in. the potentials on the control. electrodes of the tubes, so that the effective mid point of the circuit is varied, which upsets the desired symmetry. The difterence cannot be compensated by the use of a fixed balancing condenser because the amount of inequality varies as the rotor of the condenser is moved. The dissymmetry may be avoided byusing two equal condensers connected in series, but this solution is not desirable because it quadruples the ratio of the stray capacitance to the tuning capacitance, and in this field of work it is very important to keep the stray capacitance at a minimum.

Referring now to Figure 2 it will be seen that the tuning condenser consists. structurally, of two tuning condensers, 2 and 2'. There are two similar stationary portions 4: and 6, and two similar movable portions 8 and 10, cooperating with the stationary portions. The movable portions 8 and 10 are arranged for unicontrol, by being on a common shaft,

or by connection through a link 12. Although the movable portions 8 and 10 are connected mechanically, they are not connected electrically, being insulated by the insulator 12. Instead, each movable portion is connected to the stationary portion cooperating with the other movable portion, that is, the movable portion 8 is connected to the stationary portion 6 and the movable portion 10 is connected to the stationary portion 4. Connections to the condenser are made by the leads 1.4 and 16. It is obvious that the condensers are connected in parallel, but that each side of the condenser consists of a stationary portion and a movable portion, instead of two stationary portions, or two movable portions; In this way material of the same mass and distribution is connected to each lead, and therefore the stray capacitances between each side of the condenser and its'generalsun roundings, or ground, are made equal. '7

The condensers, preferablyfco nsist of int'erleaving plates of conventional form. Such amodification is illustrated in Figure 3, in which the tuning condenser'consists, structurally', of the two similar tuning condensers 20 and 22, each comprisinga stator 24 and 26, and a rotor 28 and 30. The rotors are ar ranged mechanically for unicontrol, through atuning dial 232. but the rotors are electrically insulated by an insulator'3 l. As before, each rotor is connected to the other 'stator, as shown, and the entire condenser is connected in circuit by the leads 36 and 38. The condenser is surrounded by a shielding compartment 40, and the condensers 2O an'd22 are symmetrically located with respect to the walls otthis compartment; i i V 9 It shouldbe understood that the resonant circuit shown in Figure 3 might be an output circuit,'orother symmetrical circuit, as well as an input circuit.

I claim: V.

1. A tuning reactance comprisingtwo similar stationary portlons, two similar movable 2. A single tuning condenser comprising,

structurally, two similar condensers arranged for uni-control, and means for electrically cross connecting the stators and rotors of the condensers so that the stray capacitance between the tuning condenser and its surroundings is symmetrical during movement of the rotor, while the ratio of the stray capacitance to the tuning capacitance is not increased.

3, A tuning reactance comprising two similar stationary portions, twosimilar movable portions cooperating therewith, means for s multaneously and equally moving the movable portions, means to electrically insulate the movable portions, and means connecting each of the stationary portions with that movable portion which cooperates with the other stationary portion, in order to balance the stray capacitance between the terminals of the tuning reactance and its surroundings.

4. A single tuning condenser comprising, structurally, two similar condensers arranged for uni-control, means to electrically insulate the rotors from one another, and means connecting the rotor of each condenser with the stator ot the other con denser, in order to make the stray capacitance between the tuning condenser and its surroundings symmetrical during movement of the rotors.

5. In combination, a shielding compartment and a tuning condenser, said tuning condenser comprising, structurally, two similar condensers arranged for uni-control and located symmetrically with respect to the walls of'the compartment, means to electrically insulatertbe rotors of the condensers. and means to electrically connect the rotor of each condenser-with the stator ot the other condenser, so as to make the capacitance between the tunng condenser and the shield symmetrical resonant circuit comprising, structurally,"

two similar condensers arranged symmetrr cally with respect to the walls of the compartment and mechanically connected for unicontrol, means to electrically insulate the rotors, and means to electrically connect each i of the rotors with the stator'of the other con- I denser, in order to make the stray capacitance between the tuning condenser and'the shield symmetrical during movement of the condenser rotors.

7. A tuning reactance comprising two similar stationary portions, two similar movable portions cooperating therewith, means for simultaneously and equally moving the movable portions, and connections of low impedance for cross connecting the movable and stationary portions.

8. A tuning condenser comprising, structurally, two similar condensers arranged for uni-control, and connections of low impedance cross connecting the rotors and stators of the two condensers.

9. A tuning reactance comprising two similar stationary portions, two similar movable portions cooperating therewith, means for simultaneously and equally moving the movable portions, means to electrically insulate the movable portions, and means connecting each of the stationary portions with that movable portion which cooperates with the other stationary portion.

10. A tuning condenser comprising, structurally, two similar condensers arranged for unicontrol, means to electrically insulate the rotors from one another and means connecting the rotor of each condenser with the stator of the other condenser.

11. In combination, a pair of condensers, each condenser having a stator and a rotor, a low impedance connection from the stator of one condenser to the rotor of the other condenser and a low impedance connection from the rotor of the other condenser to the stator of the one condenser.

HAROLD O. PETERSON. 

